Posted: 03/05/2014 at 18:59
OK, so weedkiller of any kind will only work if the weed has leaves and is actively growing. Glyphosate is taken up by the leaves and travels through the plant to the roots. It takes a while to see any effect - weeks rather than days. Damaging the regrowth by trampling and crushing may help absorption. "Instant" weedkillers don't kill the roots.
My technique to keep ivy under control is to pull out the long growths as necessary, and dig out roots if I want to plant in that space. Ivy usually has shallow roots, the stems root into the ground as it grows horizontally across the soil. It's certainly not impossible to dig it out, but if there's any around in your garden or the neighbour's, it will come back. It is also spread by birds, they take the berries in winter, drop the seeds and the cycle starts again. It loves shady places, growing where little else will flourish.